This non-provisional application claims priority under 35 U.S.C. xc2xa7109(a) on Patent Application No. 2001-313516 filed in Japan on Oct. 11, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a variable displacement supercharging system, and more specifically to a variable displacement supercharging system, which can determine abnormality of a variable displacement supercharger capable of changing the area of an exhaust gas flow passage toward a turbine.
2. Description of the Related Art
Conventionally, as a technique for enhancing an output of an engine, a technique, which mounts a supercharger (a turbo charger) on the engine, is known. The supercharger compresses intake air by a compressor, which is driven by the energy of the exhaust gas from the engine. The supercharger thus increases the charging efficiency of the intake air and enhances output of the engine.
A special type of supercharger, a variable displacement supercharger, has been made commercially available. This variable displacement supercharger includes a changeover valve, which opens or closes a portion of an exhaust passage according to the rotational speed of the engine. The changeover valve controls the speed of exhaust gas flowing towards a turbine of the supercharger by changing the area of the exhaust gas passage. That is, when the engine is rotated at a relatively low speed, the portion of the passage leading towards the turbine is closed to increase the flow speed of the exhaust gas flowing towards the turbine. When the engine is rotated at a relatively high speed, the flow passage leading toward the turbine is fully opened to substantially enlarge the capacity of the turbine, thus effectively making use of the energy of the exhaust gas.
However, such a variable displacement supercharger breaks down, it is impossible to control the flow speed of the exhaust gas flowing towards the turbine by using the changeover valve. Therefore, when the engine is rotated at a relatively low speed, there is a possibility that knocking occurs due to a sharp rise in supercharging pressure (pressure of intake air), while when the engine is rotated at a relatively high speed, there is a possibility that the exhaust gas pressure at the upstream of the turbine is increased so that the amount of residual gas is increased, which may cause reduction of engine output or increase the possibility of misfire.
Accordingly, as a supercharger, which can overcome such a drawback by detecting a breakdown of the variable displacement supercharger, a supercharger disclosed in Japanese Laid-open Utility Model Publication 52986/1991 is known.
In the xe2x80x9cengine provided with a superchargerxe2x80x9d disclosed therein, the supercharging pressure corresponding to the rotational speed of an engine in a normal engine running state is previously stored in a memory, the engine rotational speed and the supercharging pressure are detected, the detected supercharging pressure is compared with the stored supercharging pressure, and when the supercharging pressure becomes abnormally high, it is determined that the changeover valve has broken down.
However, in a variable displacement supercharger, even when the area of the exhaust gas passage leading towards the turbine is the same and the rotational speed, the load applied to the engine and the like are also the same, the detected values of the supercharging pressure may differ largely and thus a break down maybe erroneously determined. That is, in the variable displacement supercharger, the exhaust gas passage is opened or closed by performing the open/close operation of the changeover valve. Therefore, due to the influence of inertia of the supercharger per se, there is a time lag for the rotational speed of the turbine to reach a given rotational speed, that is, until the supercharging pressure reaches a given level. Accordingly, the detected supercharging pressure may greatly differ due to this delay of operation.
Further, as disclosed in the above-mentioned publication, the supercharging pressure, corresponding to various engine rotational speeds, are stored as a map and a plurality of determination regions are provided. If hysteresis in the changing of the changeover valve between the determination regions is provided, the influence of the degree of opening of the changeover valve immediately before operation of the valve is increased so that the time lag is further increased.
The present invention has been made to solve such a problem and it is an object of the present invention to provide a breakdown diagnosis device for a variable displacement supercharger, which can enhance accuracy of breakdown determination, thus preventing an erroneous determination and properly detecting an abnormality of the variable displacement supercharger.
The variable displacement supercharging system according to the present invention includes a variable displacement supercharging system that includes a supercharger mounted on an engine, a flow passage area changing unit mounted on the supercharger and changes an area of an exhaust gas flow passage leading towards a turbine of the supercharger, a command unit which commands at least a change of the flow passage area to the exhaust gas flow passage area changing unit to a maximum flow passage area or a minimum flow passage area based on a rotational speed of the engine and a load of the engine, a supercharging pressure detection unit which detects a supercharging pressure of the engine, an engine rotational speed detection unit which detects the rotational speed of the engine, an engine load detection unit which detects the load of the engine, a memory which preliminarily stores a target supercharging pressure based on the engine rotational speed and the engine load, and an abnormality determination unit which, when the command for change of the flow passage area is given to the flow passage area change unit by the command unit such that the exhaust gas flow passage area assumes the maximum flow passage area or the minimum flow passage area, checks for an abnormality of the supercharger by comparing the target supercharging pressure obtained from the memory based on the engine rotational speed detected by the engine rotational speed detection unit and the engine load detected by the engine load detection unit with the supercharging pressure detected by the supercharging pressure detection unit.
Accordingly, when the exhaust gas flow passage area leading to the turbine assumes either the maximum flow passage area position or the minimum flow passage area position, the operating direction of the flow passage area changing unit is restricted in one direction, wherein when the exhaust gas flow passage area is stopped at such positions, the influence of inertia to the supercharging pressure is small so that the proper supercharging pressure can be detected whereby the abnormality of the variable displacement supercharger can be properly determined based on the supercharging pressure and the target supercharging pressure.